The present invention relates to a trigger device of a tire condition monitoring apparatus. More particularly, the present invention pertains to a trigger device for a wireless tire condition monitoring apparatus that permits a driver in a vehicle passenger compartment to check conditions of tires, such as the air pressure.
Wireless tire condition monitoring apparatuses that allow a driver in a vehicle passenger compartment to check the conditions of vehicle tires have been proposed. The apparatus includes transmitters and a receiver. Each transmitter is located in the wheel of one of the tires and the receiver is located in the body frame of the vehicle. Each transmitter detects the conditions, such as air pressure and the temperature of the associated tire, and wirelessly transmits data representing the detected conditions. The receiver receives data wirelessly transmitted by the transmitters with a reception antenna and displays the conditions of the tires, for example, on a display located in front of the driver's seat.
Each transmitter is accommodated in a case provided in a tire valve. The tire valve is fitted in a valve hole of the corresponding wheel. Accordingly, the case, which accommodates the transmitter, is located in the corresponding tire (see Japanese Laid-Open Patent Publication No. 2001-174357).
A unique ID code is registered in an internal memory, for example, a ROM, of the transmitter. The ID code is used to distinguish the associated transmitter from the other three transmitters (see Japanese Laid-Open Patent Publication No. 2003-272060).
Each transmitter wirelessly transmits the ID code and the data representing the condition of the associated tire in response to a trigger signal from the trigger device. Heavy vehicles such as buses and trucks often use double tires for the rear wheels. Therefore, even if a trigger device is brought close to one of the tires of the double tire and a trigger signal is transmitted, the transmitters in both tires might respond to the trigger signal. As a result, the transmitters in both tires wirelessly transmit data representing the ID code and the condition of the associated tire at the same time. This causes the interference between the data from the transmitters. Therefore, the trigger device sometimes failed to receive data from the transmitter located in the tire to which the trigger device is brought close.